Data from: Adaptation in a variable environment: phenotypic plasticity and bet-hedging during egg diapause and hatching in an annual killifish

Two ways in which organisms adapt to variable environments are phenotypic plasticity and bet-hedging. Theory suggests that bet-hedging is expected to evolve in unpredictable environments for which reliable cues indicative of future conditions (or season length) are lacking. Alternatively, if reliable cues exist indicating future conditions, organisms will be under selection to produce the most appropriate phenotype – that is, adaptive phenotypic plasticity. Here we experimentally test which of these modes of adaptation are at play in killifish that have evolved an annual life cycle. These fish persist in ephemeral pools that completely dry each season through the production of eggs that can remain in developmental arrest, or diapause, buried in the soil, until the following rainy season. Consistent with diversified bet-hedging (a risk spreading strategy), we demonstrate that the eggs of the annual killifish Nothobranchius furzeri exhibit variation at multiple levels - whether or not different stages of diapause are entered, for how long diapause is entered, and the timing of hatching - and this variation persists after controlling for both genetic and environmental sources of variation. However, we show that phenotypic plasticity is also present in that the proportion of eggs that enter diapause is influenced by environmental factors (temperature and light level) that vary seasonally. In nature there is typically a large parameter zone where environmental cues are somewhat correlated with seasonality, but not perfectly so, such that it may be advantageous to have a combination of both bet-hedging and plasticity.

生物应对多变环境的两类适应性策略为表型可塑性（phenotypic plasticity）与赌徒避险策略（bet-hedging）。理论研究表明，当环境不可预测且缺乏可指示未来环境条件（或季长）的可靠线索时，物种更易演化出赌徒避险策略。反之，若存在可指示未来环境条件的可靠线索，生物将在选择压力下分化出最适配的表型，即适应性表型可塑性。本研究以演化出一年生生活史的鳉鱼为研究对象，通过实验探究其采用了上述哪一类适应模式。这类鳉鱼栖息于季节性完全干涸的临时水塘中，通过产下可进入发育停滞状态（即滞育（diapause））的卵，并将卵埋藏于土壤中，直至下一个雨季来临方可完成发育。本研究结果符合多样化赌徒避险策略（diversified bet-hedging，一种风险分散策略）的预期，实验证实一年生鳉鱼费氏假鳃鳉（Nothobranchius furzeri）的卵存在多维度变异，包括是否进入不同滞育阶段、滞育持续时长以及孵化时间；且在控制遗传与环境变异来源后，该变异依然显著存在。然而，研究同时发现表型可塑性同样存在于该物种中：进入滞育状态的卵的比例，会受到随季节变化的环境因子（温度与光照强度）的调控。在自然环境中，通常存在一类广泛的参数区间：环境线索与季节变化存在一定相关性，但并非完全匹配，此时同时兼具赌徒避险策略与表型可塑性或许更为有利。